Filtration



Nov. 30, 1943. w. KIERSTE'DJR -n FILTRATION Filed April 2'5, 1942 .III'

r LL. T/

Patented Nov. 30, 1943 Wynkcop Kiersted, .lr- Scandale. N. Y., assignor to The Texas Company. New YorhN. Y., a oorporation of Delaware Application april z5, 1942, seal No. 440,445

s claims. (c1. zic-201i 'Ihis invention relates to a method of and apparatus for filtration, and particularly to filtration of solidified material from a mixture of liquid and solids.

The invention contemplates a continuous ro- -5 tary type of filter with a scroll or screw conveyor discharge for the lter cake and having' means for heating the conveyor element so as to facilitate continuous discharge of the separated solid 'material from the ,filter apparatus.` The v10 'invention has particular application to the dewaxingof wax-bearing oil by a process involving filtration. l .r In dewaxing oil by filtration a wax-bearing oil is mixed with a dewaxing solvent and vchilled 15 to a. temperature in the range of about 0 F, to minus 30 F., or even lower, in order to precipitate wax constitutents of the oil as solidified hydrocarbons.I This chilled mixture is passed` to .a continuous rotary filter wherein the slidi- -20 vfied wax is separated from theliq'uid hydrocar-4 bons in the form of a filter cake, and ti'iejdel-v waxed oil is obtained as a filtrate.

The filter apparatus preferred yfor dewaxing usually comprises a totally-enclosed vacuum fil-v 25 ter of the rotatingdrum type. The filter cake of wax is scraped lor otherwise dislodged from the rotating filter surface and falls into a-horizontal screw` conveyor formed as an integral part of the filter bowl and shell. removes the dislodged filter cake from thev filter apparatus, discharging it into a suitable tank orreceiver.

There is considerable tendency at'times for the wax filter cake to clog up in the conveyor 535 and thus interrupt the continuous operation of the filter. The solid waxy material sticks or otherwise adhere! to the surface of the screw or helical impelling member which usuallyconsists 'of a shaft 40 to which'are attached a series of iiighta The adherence of solid material to the-surfaces of A the screw materially reduces its efficiency in forcing the solid'materialthrough the conveyor trough. During continued operation the quantity of waxy material adhering to the screw increasesandinashorttimethereisalargemass; of solid waxy material adhering tol and rotating with the screw, instead of permitting the surface ofthescrewtnsliporslidefreelythrmightheso solid mass and thereby push the mass forward throush the trough of the conveyor. A In dewaxingitfis desirable to operate so that theiilter cakeis as free from solvent as possible as it leaves the filter surface and fallsinto 55 The conveyor thus C30 the conveyor. However, the less solvent thecake contains the greater the tendency towardv sticking in the conveyor. The present invention is of particular advantagev in dewaxing so as to discharge a wax cake relatively l'ow in solvent content.

Therefore, my invention involves maintaining a fluid film between the solid waxy mass and the surface of the screw to avoid the 'aforesaid sticking action and to permit the surface of the screw to slide freely through the solid mass. -In this way the screw operates at full ei'ilciency and can move the solid mass fforwar'd through the trough of the conyeyor without substantial liquefaetion of the wax.

It is desirable to avoid liquefying any substan-y tial amount of the waxy mass while it remains in the conveyor since this would involve the' liberation of some heat in the filter hood and this is highly undesirable because it results in objectionable warming ofthe atmosphere within the hood.

Such warming has been found to interfere with the eiiicient operation of the filter in dewaxing lubricatingoil stocks or in separating wax from wax-bearing mixtures.

Inv accordance-1'v withy my invention the helical screw or'scroll element of the filter discharge conveyor is ydesignedto receive a limited amount of heat from a suitable source and transfer it to Lthe waxy mass moving through the 'conveyor'.

In a preferred form of the invention a hollowV screw or scroll is employed with means for passing a iiuid heat carrying medium through the interior of the element'. The heat carrying medi'um advantageously comprises warm solvent liquid stripped from the wax concentrate or from the d ewaxed filtrate in a subsequent stage ofthe process. In order to describe the invention more fully reference will now be made to the figures of the accompanying drawing.

. In the drawing Figs. .l and '2 represent; semi-V 'sectional and diagrammaticviewsof a'`fi4`zintiu-v ,o ous rotary drum type of filtery such as-isus'ed 45, the -dewaxing of mineral oil and which requires no detailed description. l.

As illustrated in Figs. 1 and 2, the filter comprises a shell l, the lower portion of which forms a lter bowl into which the mixture to be ltered is introduced through-'a pipe 2.

VA hollow drum 3 whose cylindrical surface forms the filtering surface is rotatably supported withinthe shell I. The cylindrical mtelin Bur'- face is divided into separate sections or seg-- ments, each communicating by'means of con-l duits with a hollow shaft 4 .which supports the drum 3. One end of the shaft 4 terminates in ar conventional type of filter valve through which provision is made for withdrawing the filtrate and wash filtrate, and also forintroducing blowback gas for dislodging the filter cake from the filter surface. y

Sprays 5 communicating with a source of wash solvent are provided in the upper portion of the filter shell for introducing a spray wash for washing the lter cake in situ and prior to dislodgment from the filter surface.

'I'he washed filter cake is scraped from the filter surface by a suitable scraper 6 and vdrops into a conveyor trough or conduit 1. The conduit 'I extends horizontally along the side of the filter shell. f

Within the conduit 'I is a hollow scroll 8 supported on a shaft 9.

The shaft 9 is rotatably supported in stuffing boxes I provided in each end of the conduit 1. One end of the shaft 9 is coupled by means of a coupling I I to a motor I2 and by which means the scroll is subjected torotation within the conduit 1. u

The shaft 9 is hollow and ports I3 and I4 provide communication between the interior of the shaft 9 and the interior of the ends respectively of the hollow spiral 8. A restrictive orifice 9a is placed within the interior of the shaft 9 so as to cause flow of heat carrier fluid through the hollow spirals as well as through the hollow shaft.

A stationary box I surrounds shaft 9 at one end, suitable stuiiing boxes I6 being provided to prevent escape of kfluid between thesurface of the rotating shaft and the adjacent bearing surface of the box I5. A port I'I provides fluid access to the interior of the hollow shaft 9 with-- in the box I5. Y l

The box I5 is provided with a pipe connection I8 through which fluid may be withdrawn from or introduced to the interior of the box.

The opposite end of the shaft. 9 terminates in4 a stuffing box I9 and through which means-it communicates withl the open end of a corresponding stationary pipe 2l).l The pipe 20 provides-means for introducing fluid to or ,Withdrawing it from the hollow end of the shaft 9.

Thus, in actual operation a heat carrier fluid,

either liquid or gaseous, is caused to fiow through the interior of the scroll 8 continuously during its rotation. The filter cake material still in substantially solid form is discharged from the conduit 'l through a chute 2|. 3

The heat carrier fluid may flow through the hollow scroll in either direction, as desired.

Fig. 3 illustrates an adaptation ofv the above described filter apparatus tothe dewaxing of wax-bearing mineral lubricating oil. The wax-bearing oil, from a source not shown,

Vis conducted through a pipe 30 to. a mixer 3|.

wherein it is mixed with dewaxing solvent liquid introduced through a pipe 32., also from a source not shown. p v

The solvent, for example, may consist of a mixture of .about 40% methylethyl ketone and 60% commercial benzol. The solvent Vmixture is mixed with the wax-bearing oil in the prodrocarbons. The chilled mixture is then introduced to the filter bowl of 4a rotary filter, such as illustrated in Figs. 1 and 2.

The resulting filtrate, comprising solvent liquid mixed with dewaxed oil, having a pour test of about 0 to minus 10 F. is withdrawn through a pipe 34, through which it is conducted either to a receiver or to a stripper, for `recovering the solvent. i

The wax cake formed in the filter is discharged I into the conduit 'I containing the hollow heated scroll 8. From the conveyor the waxcake is discharged through the chute 2i into a receiver v 35. The wax cake is subjected to further heat- Y to a stripper 31 for recovery ofthe solvent.

The solvent vapors are passed through a condenser 38 and a suitable portion of distillate at a temperature of about 110 F. is conducted through a pipe 39 communicating with the pipe I8 and through'which it is introduced to the box I5.

The temperature and amount of warm solvent conducted through the interior of the hollow screw i`s controlled so as to maintain the skin temperature of the flights ofthe screw .'ust high enough to prevent sticking of the solid waxy material to the metal. For example, this skin temperature may range from about 60 to 90 F. It`is contemplated that the skin temperature is merely sufficient to form a relatively thin film of liquid, such liquid consisting largely of solvent present in the solid waxy mass passing through -the conveyor. This film of liquid keeps the metal surface wet, thereby facilitating its movement through the waxy mass.

From the box-I 5 the solvent distillate flows into -the interior of the hollow shaft 9 and passes cake or added as additional diluent to thewaxbearing charge and solvent mixture at the out- A let of. chiller 33.

Thus, the wax cake', is received in the `receiver L35 ait-substantially the same temperature as that at which it leaves the filter surface or at a temperature which is usually not more than i about 2 or 3 degrees higher than thetemperature at which it leaves the filter surface and enters the trough of the conveyor.

While the filter apparatus has been described .as particularly applicablel to the dewaxing of wax-bearing lubricating oil, it is contemplated .that it is applicable toother industrial uses involving the filtration of liquefiable solid materials from mixtures of such solids with liquids.

'I'he specific means described above for supplying heat to the rotating scroll may vary from that described. Also the screw may be in Athe form of a hollow shaft with solid.fins or flights.

The present application is a continuation-inpart of my pending application, Serial No. 317,835, filed February 8, 1940, for Filtration.'

' Obviously many modifications and variations of the invention as herei'nbefore set forth may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the ap ture of oil and wax which comprises chilling the mixture to a temperature sufficiently low to solidify wax, filtering the chilled mixture in afilter provided with a filter cake discharge conveyor having a hollow impelling screw, sai'd conveyor being arranged to conduct filter cake, .dislodged from the filter surface, from the interior to the exterior of the filter housing, passing wann of s'aid wax during passage through the conveyor, discharging the solidified wax from said ,conveyor at a temperature not substantially above the temperature at which the filter cake enters the conveyor, and separately discharging filtrate from the filter.

2. The method of separatingwax from a mixture of oil and wax which comprises chilling the mixture to a ytemperature sufiiciently low to solidify wax, filtering the chilled mixture in a filter provided with a filter cake discharge conveyor-having a hollow impelling screw, said conveyor being arranged to conduct filter cake, dislodged from the filter surface, from the interior to the exterior of the filter housing, passing through the hollow screw a stream of fluid in an amount and at a temperature sufficient. to. maintain substantially all of the surface of the screw which is in contact with wax at a temperature of about 60 to 90 F. and such lthat sticking of solid wax to said surface is substantially avoided, discharging solidified wax from filter provided with a filter cake discharge conveyor having a hollow impelling screw, said cony veyor being arranged to conduct filter cake, dislodged from the filter surface, from the interior to the exterior of the iilter housing, passing through the hollow screw a stream of fluid in an amount and at-a temperature sufficient to main- V tain substantially all of the surface of the screw.

which is in contact with'wax at a temperature not in excess of.about 90 F., maintaining said surface wet with a relatively thin film of liquefied filter cake sufficient to prevent substantial t sticking of the solid cake to the surface, discharging the cake in solid form from the conveyor at a temperature not substantially above the temperature at which it enters the conveyor,

and separately discharging filtrate from the filter.

4. 'I'he method of dewaxing wax-bearing'lubricating oil which comprises mixing the wax-bearing oil with a normally liquid solvent chilling the mixture to 'a teni'perature sufficiently low to solidify wax, filtering the chilled mixture in av filter providedv with a conveyor having a hollow screw, said conveyor being adjacent the filter element within the filter bowl for receivingl the ,wax cake removed from the filter element and for discharging the received wax from the filter,

` continuously .passingv through the hollow screw a'stream of fluid at a temperature not in excess of about 110 F., so .as to prevent adherence of solid waxto the screw, discharging the cake in solid form from the conveyor at a temperature not substantially above the temperature at which it enters the conveyor, and separately discharging the filtrate from the filter.-

-. 5. 'I'he method of dewaxing wax-bearing lubricating oil which comprises mixing the wax-bearing oil witha normally liquid solvent chilling the mixture to atemperature suiiiciently low to solidify wax, filtering the chilled'mixture in a filter provided with a conveyor having a hollow screw,'said conveyor being adjacent lthe filter element within the filter bowl forI receiving the wax cake still retainingsome liquid and for discharging the received wax from the filter, dis- "tilling retained liquid from the discharged wax cake, continuously passing through said .hollow -screw a stream Aof said distilled liquid at a telnperature'not in excess of about 110 F., so as to prevent adherence of solid wax to the screw, discharging the cake in solid form from the conveyor at a temperature not substantially-above the temperature at which it enters the conveyor and separately dischargingthe filtrate from the filter.

6. The method of separating, constituents `which can be solidified from a liquid mixture within the conveyor, controlling the amount of heat added so as to maintain substantially all of the surface of the screw which is in contact with the cake suiiiciently warm to preventsubvs'tantial sticking of 'cake to said surface but insufficient to cause substantial liquefaction of the cake during passage through the conveyor, discharging the filter cake solids from the conveyor without substantial liquefaction and separately discharging liquid from the filter asiiltrate.

7. The method of separating constituents which can be solidified from a liquid mixture containing such constituents which comprises chilling thev mixture to a temperature sufliciently low to effect solidiiication of said constituents in at least substantial amount, filtering the chilled mixture ofliqud and'solids in a filter provided with ascrew conveyor discharge, said conveyor .being arranged to conduct filter cake, dislodgefi from the filter surface, from the interior to the vexterior of/,the filter housing, maintaining substantially all of the surface of said screw which Iis incontact with the cake wet with a film of liquid suiticient to prevent sticking of cake to said surface but insufiicient to cause substantial liquefactionof said cake-during passage through the conveyor, discharging the filter cake solids from the conveyor without substantial liquefaction and separately discharging liquid from the filter as iiltrate.- g

8. The .method of -s eparating constituents which can besolidifled from a liquid mixture containing such constituents, which comprises being arranged to conduct dislodged lter cakev from the interior tothe exterior of the filter ture at which the cake enters the conveyor but insufiiciently high to cause substantial liquefaction of the `cake, maintaining said screw surface wet with a film of liquid formed from the cake such that sticking of cake to the screw surface.

is substantially avoided, discharging the filter cake solids from the conveyor without substan- 1 tial liq'uefaction and separately discharging liquid from the filter as filtrate.

wYNKooP KIERSTED, .ni 

